• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.127-133
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• 2021

A recent study of people physically falling focused on analyzing the motions of the falls using a recurrent neural network (RNN) and a deep learning approach to get good results from detecting 2D human poses from a single color image. In this paper, we investigate a detection method for estimating the position of the head and shoulder keypoints and the acceleration of positional change using the skeletal keypoints information extracted using PoseNet from an image obtained with a low-cost 2D RGB camera, increasing the accuracy of judgments about the falls. In particular, we propose a fall detection method based on the characteristics of post-fall posture in the fall motion-analysis method. A public data set was used to extract human skeletal features, and as a result of an experiment to find a feature extraction method that can achieve high classification accuracy, the proposed method showed a 99.8% success rate in detecting falls more effectively than a conventional, primitive skeletal data-use method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.880-887
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• 2020

This study was conducted to investigate the running stability of a high-speed train operated in a tunnel and an open field when external forces such as wind pressure and train crossings were applied to the vehicle. With no external force, the running stability at 400 km/h was examined, and the wheel weight reduction ratio, lateral pressure of the axles, and derailment coefficient satisfied the criteria of the technical standards for a high-speed train. When the distance between the centers of the tracks is 4.6 m, the external force caused by train crossing slightly affects the lateral acceleration of the vehicle but does not significantly affect the wheel weight reduction rate, lateral pressure, and derailment coefficient in a tunnel and open filed. When the distance is 4.6~5.0 m, the wheel weight reduction ratio, lateral pressure, and derailment coefficient satisfy the criteria with 20 m/s wind. When the wind speed was 30 m/s, the derailment coefficient satisfied the criteria, and the other variables exceeded them. It is predicted that a high-speed train can be operated safely at 400 km/h with wind speed of up to 20 m/s, and it should be slowed down at a wind speed of 30 m/s.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.77-86
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• 2020

In this study, the importance of implied strength correction for shallow depths at a region of moderate to low seismicity with primary focus on its effect upon site natural period and mean period of the ground motion is investigated. In addition to the most commonly used Modified Kondner-Zelasko (MKZ) model, this paper uses a quadratic/hyperbolic (GQ/H) model that can capture the stress - strain response at large strains as well as small strain stiffness dependence. A total of six site profiles by downhole tests are used and 1D site response analyses are performed using three input motions with contrasting mean periods. The difference between non-corrected and corrected analyses is conditional on the site period as well as mean ground motion period. The effect of periods is analyzed by correlating them with the effective peak ground acceleration, maximum shear strains and amplification factors. The comparative study reveals that the difference is more prominent in soft sites with long site periods. Insignificant differences are observed when soil profiles are subjected to ground motion with very short mean period.

• Journal of the Korean earth science society
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• v.41 no.6
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• pp.647-657
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• 2020

Infrasound signals associated with the 29 May 2004 offshore Uljin earthquake (Mw 5.1) were recorded at infrasound arrays of CHNAR (epicentral distance of 321 km) and TJNAR (256 km). Back-azimuths, indicating the directions to source locations, varied more than 28° broadly for the long-lasting signals over several minutes. From the analysis of the back-projecting location method and attenuation correction for infrasound propagation, the infrasound waves were to be generated by the interaction (diffraction) between seismic waves and topography in an area of ~4,600 ㎢ connecting the Samcheok-Uljin-Pohang regions. The maximum sound source pressure (BSP) was estimated to be 11.1 Pa. This result was consistent with the peak sound pressure (PSP) calculated by the Rayleigh integral approximation to the peak ground acceleration (PGA) dataset. In addition, the minimum PGA that was detectable at the two arrays was estimated to be ~3.0 cm s-2. Although the earthquake occurred offshore, diffracted infrasound signals were effectively generated by ground motions when seismic surface waves passed through high-topographic regions in the eastern Korean Peninsula. The relationship between infrasound source pressure and PGA can be applicable to characterize the ground motions in areas with insufficient seismological observatories.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.126-134
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• 2020

In the case of an earthquake, the fluid storage structure generates hydraulic pressure due to the fluctuation of the fluid. At this time, the hydraulic pressure of the fluid changes not only the peaked acceleration of the earthquake but also the sloshing height of the fluid free water surface. Factors influencing this change in load include the shape of the seismic wave, the maximum seismic strength, the size of the fluid storage structure, the width of the structure, and the height of the fluid. In this study, the effect of the ratio between the height of the fluid and the width of the structure was investigated on the fluctuation characteristics of the fluid. 200mm and 140mm of fluid were placed in a water storage tank with a width of 500mm, and a real seismic wave was applied to measure the shape of the fluctuation of the fluid free water surface. The similarity between the experiment and the analysis was verified through the S.P.H(Smoothed Particle Hydrodynamic) technique, one of the numerical analysis techniques. It was confirmed that the free water surface of the fluid showed a similar shape, through comparison of experiment and analysis. And based on this results, SPH technique was applied to analyze the fluctuation shape of the fluid free water surface while varying the ratio between the fluid height and the structure width. An equation to predict the maximum and minimum heights of the fluid free water surface during an earthquake was proposed, and it was confirmed that the error between the maximum and minimum heights of the fluid free water surface predicted by the proposed equation was within a maximum of 3%.

• Journal of the Korean institute of surface engineering
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• v.53 no.6
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• pp.271-279
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• 2020

Non-ferrous metals, widely used in the mechanical industry, are difficult to machine, particularly by drilling and tapping. Since non-ferrous metals have a strong tendency to adhere to the cutting tool, the tool life is greatly deteriorated. Diamond-like carbon (DLC) is one of the promising candidates to improve the performance and life of cutting tool due to their low frictional property. In this study, a sacrificial DLC layer is applied on the hard nitride coated drill tool to improve the durability. The DLC coatings are fabricated by controlling the acceleration voltage of the linear ion source in the range of 0.6~1.8 kV. As a result, the optimized hardness(20 GPa) and wear resistance(1.4 x 10-8 ㎣/N·m) were obtained at the 1.4 kV. Then, the optimized DLC coating is applied as an sacrificial layer on the hard nitride coating to evaluate the performance and life of cutting tool. The Vickers hardness of the composite coatings were similar to those of the nitride coatings (AlCrN, AlTiSiN), but the friction coefficients were significantly reduced to 0.13 compared to 0.63 of nitride coatings. The drilling test were performed on S55C plate using a drilling machine at rotation speed of 2,500 rpm and penetration rate of 0.25 m/rev. The result showed that the wear width of the composite coated drills were 200 % lower than those of the AlCrN, AlTiSiN coated drills. In addition, the cutting forces of the composite coated drills were 13 and 15 % lower than that of AlCrN, AlTiSiN coated drills, respectively, as it reduced the aluminum clogging. Finally, the application of the DLC sacrificial layer prevents initial chipping through its low friction property and improves drilling quality with efficient chip removal.

• Journal of Advanced Navigation Technology
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• v.25 no.1
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• pp.68-77
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• 2021

In this paper, a GPS/MEMS IMU integrated navigation receiver module capable of operating in a high dynamic environment is designed and fabricated, and the results is confirmed. The designed module is composed of RF receiver unit, inertial measurement unit, signal processing unit, correlator, and navigation S/W. The RF receiver performs the functions of low noise amplification, frequency conversion, filtering, and automatic gain control. The inertial measurement unit collects measurement data from a MEMS class IMU applied with a 3-axis gyroscope, accelerometer, and geomagnetic sensor. In addition, it provides an interface to transmit to the navigation S/W. The signal processing unit and the correlator is implemented with FPGA logic to perform filtering and corrrelation value calculation. Navigation S/W is implemented using the internal CPU of the FPGA. The size of the manufactured module is 95.0×85.0×.12.5mm, the weight is 110g, and the navigation accuracy performance within the specification is confirmed in an environment of 1200m/s and acceleration of 10g.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.5
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• pp.103-110
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• 2020

In the recent seismic design code KDS 41 17 00, selection and modification procedures of ground motions which are used for nonlinear dynamic analyses were adopted. However, its practical applications are still limited due to the lack of literatures. This paper introduces case studies which used site-response analyses to select and modify ground motions for nonlinear dynamic analyses. Based on the case studies, design criterion for site-response analyses were reviewed thoroughly in the viewpoint of practical applications. It was found that design requirements related with bedrock motions are too conservative that ground motions are selected and modified in the excessive manner. It is especially true for low-rise building structures with period ranges including acceleration-sensitive regions. Even though surface motions have shown appropriate responses, such building structures have to re-select and re-modify ground motions based on pre-analysis procedures rather than post-ones according to the current seismic design code. Also, it was observed that building structures with soft soils under strong ground motions need more comprehensive investigations on soil properties and efficient analysis methods in order to perform site-response analyses. This is due to the fact that lack of reliabilities on soil properties and analysis methods could result in unstable site-responses.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.24 no.6
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• pp.1-13
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• 2021

This study was performed to investigate the ecosystem service patterns in relation to climate change acceleration utilizing big data analysis. This study aimed to use big data analysis as one of the network of views to identify convergent thinking in two fields: climate change and ecosystem service. The keywords were analysed to ascertain if there were any differences in the perceiving problems, policy direction, climate change implications, and regional differences. In addition, we examined the research keywords of each continent, the centre of ecosystem service research, and the topics to be referred to in domestic research. The results of the analysis are as follows: First, the keyword centrality of climate change is similar to the detailed indicators of The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) regulations, content, and non-material ecosystem services. Second, the cross-analysis of terms in two journals showed a difference in value-oriented point; the Ecosystem Service Journal identified green infrastructure as having economic value, whereas the Climate Change Journal perceives water, forest, carbon, and biodiversity as management topics. The Climate Change Journal, but not the former, focuses on future predictions. Third, the analysis of the research topics according to continents showed that water and soil are closely related to the economy, and thus, play an important role in policy formulation. This disparity is due to differences in each continent's environmental characteristics, as well as economic and policy issues. This fact can be used to refer to the direction of research on ecosystem services in Korea. Consistent with the recent trend of expanding research regarding the impacts of climate change, it is necessary to study strategies to scientifically predict and respond to the negative effects of climate change.

• Land and Housing Review
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• v.13 no.1
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• pp.141-150
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• 2022

Responding to the increasing demand for research on seismic resistance of structures triggered by a large-scale earthquake in Korea, the Ministry of the Interior and Safety revised the typical application of the existing seismic design standards with the national seismic performance target enhanced. Therefore, in this paper, the dam body of the aged Test-Bed and the penstock with fluid were modeled by the three-dimensional finite element method by introducing several variables. The current seismic design standard law confirmed the safety of the dam structure and penstock against seismic waves. As a result of the 3D finite element analysis, the stress change due to the water impact of the penstock was minimal, and it was confirmed that the effect of the hydraulic pressure was more significant than the water impact in the earthquake situation. When the hydrostatic pressure is in the form of SPH, it was analyzed that the motion of the fluid and the location of stress caused by the earthquake can be effectively represented, and it will be easier to analyze the weak part. As a result of the analysis, which considers penstock's corrosion, the degree of stress dispersion gets smaller because the penstock is embedded in the body. The stress result is minimal, less than 1% of the yield stress of the steel. In addition, although there is a possibility of micro-tensile cracks occurring in the inlet of the dam, it has not been shown to have a significant effect on the stress increa.